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Cellulitis

Table of Contents
  • Definitions
  • Key Points
  • Triage
  • Causes
  • Clinical features
  • Investigations
  • Differential Diagnosis 
  • Management
  • References

Definitions #

  • Cellulitis: bacterial infection of the skin and soft tissue that can affect the epidermis, dermis, hypodermis and superficial fascia1
  • Erysipelas: superficial, more commonly occurring in children and characterised with raised and sharply demarcated inflammation, with clear margins differentiating from uninvolved skin2
  • Folliculitis: localised inflammation of a hair follicle or sebaceous glands, limited to the epidermis4
  • Furuncles: deep folliculitis beyond the dermis with abscess formation in the subcutaneous tissue4

Carbuncles: confluent folliculitis, forming an inflammatory mass; abscess and skin necrosis may be present4

Key Points #

  • Antibiotics are not needed in young, healthy patients with uncomplicated cellulitis
  • In the more at-risk population, antibiotics, leg elevation and rest are generally sufficient to treat most cellulitis
  • Have a high index of suspicion for necrotising fasciitis in patients who have haemodynamic instability, pain out of proportion to appearance, dusky skin and hard subcutaneous tissue with crepitus on palpation
  • In necrotising fasciitis, the cornerstones of management are early commencement of antibiotic therapy while preparing for urgent surgical debridement.

Triage #

If uncomplicated cellulitis: Attend within hours 

If complicated cellulitis: Attend within 30 minutes and refer for review by senior clinician and refer to general surgery for expert advice.necrotising soft tissue infection/necrotising fasciitis, or Fournier’s gangrene, or orbital cellulitis or when the patient is hemodynamically unstable secondary to sepsis

Causes #

The following are distinct diagnostic features and common presentations for the respective organisms however are not definitive causes(3). 

Non-purulent

  • Streptococcus species (eg group B, C or G)

Purulent

  • Staphylococcus aureus

Exposure specific 

Penetrating trauma or ulceration

  • Staphylococcus aureus

Fresh water exposure

  • Aeromonas species

Salt water exposure

  • Vibrio species

Clinical features #

Red Flags

Necrotising soft tissue infection/Necrotising fasciitis: 

  • Rapid onset and progression
  • Severe pain out of proportion to appearance
  • Skin duskiness/discolouration
  • Numbness
  • Hard subcutaneous tissue that extends beyond superficial involvement
  • Subcutaneous crepitus
  • Haemodynamic instability
  • High fever, disorientation 2
    • Delirium could also be secondary to simple cellulitis in the elderly population 

Fournier’s gangrene: necrotising fasciitis of the external genitalia that can spread rapidly to the anterior abdominal wall and gluteal muscles1

Orbital cellulitis: External eye muscle ophthalmoplegia and proptosis, decreased visual acuity and chemosis, blurred or double vision2

Most common

  • Redness; can be well-demarcated or generalised
    • Mark area of redness/take daily photos to monitor progression
    • Beware that cellulitis will usually worsen in the first 102 days before improving
  • Swelling
  • Heat
  • Tenderness
  • Blistering

Systemic:

  • Fever/malaise
  • Unilateral involvement
  • Lymphadenopathy 

Further history to assess risk factors2

  • Venous insufficiency
  • Diabetes mellitus
  • Immunosuppression 
  • Chronic kidney disease
  • Obesity
  • Eczema
  • Foreign body/trauma

Investigations #

Initial investigations2 

InvestigationSignificance
FBEElevated WCC suggests infection 
CRPElevated CRP represents inflammation (note delayed response)
UEC/LFTAKI secondary to shock indicates end organ damage and will also influence antibiotic choice

Further investigations2

InvestigationIndication
Wound MCSSigns of broken skin and discharge present, worsening infection, poor healing/not healing as expected and recurring infection
Cultures and sensitivities will determine antibiotic choice
Blood culturesBacteraemia suspected
Positive cultures indicate bacteraemia (can occur secondary to cellulitis)
Soft tissue ultrasound*Suspected foreign body at site of infectionSuspected complex abscess (perianal abscesses, polymicrobial or resistant pathogens), necrotising fasciitis Assessment of size/extent of abscess
X-rayEvaluation of osteomyelitis in prolonged cellulitis or long-standing non-healing ulcers
CT/MRI*Usually only necessary for complex skin abscesses and associated complications (osteomyelitis, necrotising fasciitis)

(*) indicates discussion with senior clinician 

Referrals

General surgery/ Plastics (depending on hospital)Consider referral if signs of skin abscesses, recurrent skin abscesses, complex abscesses, increased risk of complications or necrotising skin infection
Infectious diseasesConsider referral if polymicrobial cellulitis present

Differential Diagnosis  #

  • Deep venous thrombosis 
  • Stasis dermatitis 
  • Superficial thrombophlebitis 
  • Drug reactions 
  • Insect bites 
  • Vasculitis 
  • Acute gout

Management #

Cellulitis with haemodynamic instability5

Call out box on haemodynamic instability: systemic features with lactic acidosis and sBP<90mmHg (septic shock if not responsive to fluid resuscitation)

If necrotising skin and soft tissue is suspected, surgical debridement of devitalised tissue and urgent antibiotic therapy are essential; refer to general surgery/plastics.

Meropenem 1 g IV, 8 hourly OR Piperacillin + tazobactam 4+0.5 g IV, 6 hourly

PLUS 

Vancomycin 25 to 30 mg/kg IV, as a loading dose (link to vancomycin dosing page)

PLUS

Clindamycin 600 mg IV, 8 hourly OR Lincomycin 600 mg IV, 8 hourly

If infection is associated with a wound that has been immersed in water, ciprofloxacin is included in the empirical regimen, because Aeromonas isolates often produce carbapenemase enzymes.

A total duration of two weeks of therapy (oral + IV) is recommended.

Cellulitis with systemic features3

Call out box on systemic features: Two or more of the following: T >38°C OR <36°C, HR >90bpm, RR>20 breaths/minute, WCC>12 OR <4 but not associated haemodynamic instability (hypotension, septic shock or rapid progression of systemic features)

Erysipelas or non-purulent (S. pygenes suspected) 

Benzylpenicillin 1.2 g IV, 6 hourly

Purulent (Staphylococcus aureus suspected) 

Flucloxacillin 2 g IV, 6 hourly

MRSA suspected

Vancomycin IV (link to vancomycin dosing page) 

OR

Clindamycin 600 mg IV, 8 hourly

OR

Lincomycin 600 mg IV, 8 hourly

Cellulitis without systemic features3

Erysipelas or non-purulent (S. pygenes suspected) 

Phenoxymethylpenicillin 500 mg orally, 6 hourly for 5 days 

OR

Procaine benzylpenicillin 1.5 g IM, daily for at least 3 days

Purulent (Staphylococcus aureus suspected)

Dicloxacillin 500 mg orally, 6 hourly for 5 days

OR

Flucloxacillin 500 mg orally, 6 hourly for 5 days

OR

Cefalexin 500 mg orally, 6 hourly for 5 days
liquid formulation is better tolerated in the paediatric population

MRSA suspected

Trimethoprim + sulfamethoxazole 160+800 mg orally, 12 hourly for 5 days

OR

Clindamycin 450 mg orally, 8 hourly for 5 days

References #

  1. Amboss [Internet]. [place unknown]; publisher unknown]; Amboss; 2021. Skin and soft tissue infections; 2021 [cited 2021 Aug 29]; Available from: https://www.amboss.com/us/knowledge/Skin_and_soft_tissue_infections/
  2. BMJ Best Practice. Cellulitis and Erysipelas [Internet]. England and Wales; BMJ Publishing Group Limited; 2021 [last updated 2021 Jun 18; cited 2021 Aug 29], Available from: https://bestpractice.bmj.com.acs.hcn.com.au/topics/en-gb/3000172?q=Cellulitis%20and%20erysipelas&c=recentlyviewed
  3.  eTG complete [Internet]. Melbourne (Vic): Therapeutic Guidelines Ltd; 2019. Cellulitis and erysipelas [last updated 2021 Aug; cited 2021 Aug 29], Available from: https://tgldcdp.tg.org.au.acs.hcn.com.au/viewTopic?topicfile=cellulitis-erysipelas&guidelineName=Antibiotic&topicNavigation=navigateTopic#toc_d1e460 
  4. Stevens DL, Bisno AL, Chambers HF, et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update by the Infectious Diseases Society of America. Clinical Infectious Diseases. 2014 July 15; 59(2): e10–e52
  5. eTG complete [Internet]. Melbourne (Vic): Therapeutic Guidelines Ltd; 2019. Necrotising skin and soft tissue infections [last updated 2019 April; cited 2021 Aug 29], Available from: https://tgldcdp.tg.org.au.acs.hcn.com.au/viewTopic?topicfile=skin-soft-tissue-necrotising-infections&sectionId=abg16-c136-s3#toc_d1e143
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Dr Anita Ng

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Updated on April 13, 2023
Table of Contents
  • Definitions
  • Key Points
  • Triage
  • Causes
  • Clinical features
  • Investigations
  • Differential Diagnosis 
  • Management
  • References

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